Method and apparatus for producing ions



Sept. 28, 1954 MA K 2,690,515

METHOD AND APPARATUS FOR PRODUCING IONS Filed July 22, 1953 2 sheets-sheet 1 I 1 I @a- B F/g.

F/g. a

avwwm Julian E. Mack Sept. 28, 1954 J. E. MACK 2,690,515

METHOD AND APPARATUS FOR PRODUCING IONS Filed July 22, 1953 2 Sheets-Sheet 2 H k H Patented Sept. 28, 1954 UITED METHGD AND APPARATUS FOR PRODUCING IONS Julian Ellis Mack, Madison, Wis, assignor to the United States of America as represented by the United States Atomic Energy Commission Application July 22, 1953, Serial No. 382,493

This invention is a continuation-in-part of the invention disclosed in application S. N. 588,055, filed April 12, 1945, now abandoned, and relates to methods and apparatus for producing gaseous ions, especially to methods and apparatus for producing gaseous ions of metals useful in the ionic separation of their isotopes. More particularly this invention relates to new and improved methods and apparatus for producing gaseous ions of metals such as, for example, copper, cobalt or uranium, under vacuum by establishing an electric arc discharge in vacuum and continuously feeding into the arc discharge a powder of the particular metal.

One type of isotope separator in which the ion producing apparatus and method of ion production of the present invention may be advantageously used may be found described and claimed in United States Patent 2,606,291 of Robert R. Wilson, filed March 11, 1946.

This type of isotope separator may consist essentially of an evacuated and sealed chamber, that may be cylindrical and of predetermined proportions adapted to enclose at one end thereof the apparatus of the present invention for producing the gaseous ions together with an accelerating electrode for withdrawing and accelerating the ions produced in said apparatus. This chamber may also comprise means for sup-- porting in insulated relationship a plurality of bunching electrodes spaced from each other and from said accelerating electrode of the ion producing apparatus. These bunching electrodes are maintained at the same steady state potential to provide a field-free space intermediate the accelerating electrode and first part of the buncher electrode structure, for the flow therethrough of the accelerated ionized particles. An alternating potential of radio-frequency and small amplitude, preferably saw-tooth in wave form, is applied to one of said bunching electrodes periodically impressing increments of velocity both positive and negative upon the ionized particles passing therethrough, to cause these particles to bunch together in accordance with their mass. An analyzer comprising deflector electrodes having a radio-frequency potential applied thereto derived preferably from the radio-frequency source applied to the buncher, is likewise supported within the chamher but at a distance from the buncher electrodes to provide a substantial field-free r gion of definite length immediately following and adjoining said bunoher electrodes. The radio-frequency potential applied to this analyzer is synchronized with the radio-frequency potential ap plied to the electrodes to deflect, for example, the preferred enriched group of ions of the desired isotope into a collecting pocket or cup positioned at or adjacent the end of said chamber.

That the operation of ionic mass separating devices of the type similar to that described above (or of other types including magnetic separating structures) may be effectively employed on a production basis it is essential that the ion source utilized in the device be capable of producing suitable gaseous ions of the particular metal in a sufficient quantity and for sufliciently long continuous periods to permit a large scale separation of their isotopes.

The apparatus as described above is designed for the separation of a selected isotope from a source metal containing a mixture of isotopes such as cobalt 59 and 60, copper 63 and 65, zinc isotopes 65, 66, 6'7, 68 and '70 and uranium isotopes such as 235 and 238. For such purposes and particularly to afford a substantial yield of the desired isotope or isotopes, ion beams of very high content are required. Likewise, especially for quantity production the ion source should be capable of operating continuously and uniformly for long periods of time.

It has been found from prior investigation conducted in an effort to develop apparatus for producing gaseous ions of a source metal through the employment of the metal itself as distinguished from apparatus for producing gaseous ions through the employment of the more readily vaporizable salts of the source metal that the early difficulties encountered in finding a material capable of holding metal to be vaporized could be avoided by supporting a small and predetermined quantity of the source metal upon a grid-like anode of suitable refractory metal, tungsten for example. By so maintaining the concentration of the source metal sufliciently low relative to the amount of tungsten constituting the support it is possible to restrict the heretoiore deleterious efiect produced by the alloying of the source metal with the refractory metal of the anode, which otherwise would result the equivalent of a reduction in the melting temperature of the anode, (since the alloy melts at a lower temperature than tungsten alone) with consequent rapid erosion and destruction of the anode. Apparatus employing this basic discovery to permit continuous operation for long periods without serious contamination of the arc electrodes (c. g. without deleterious alloying) have been developed and may be found disclosed in 3 the following applications for Letters Patent of the United States, Serial No. 330,952 (48), filed January 13, 1953, now Patent No. 2,677,060 and Serial No. 334,0l3(48), filed January 29, 1953.

While the operation of the devices for developing gaseous ions from a particular metal of a type similar to those disclosed in the aforementioned applications is satisfactory from the point of view that the contamination of the arc electrodes is restricted to give prolonged periods of operation, these devices have their attendant disadvantages that are avoided in the present invention. It has now been discovered that the contamination of the arc anode present in this prior type of ion source produced by depositing on to the anode the particular source metal to be vaporized and ionized, may not only be restricted by controlling the amount of metal contacting the arc anode at any one time but may now be entirely eliminated by continuously feeding into the arc discharge in a region adjacent the anode, but out of contact therewith, a powder of the particular metal which is vaporized by the heat of the arc, particularly the radiant heat of the arc anode. Thus it has been possible to obtain still longer periods of continuous operation and the disadvantages concomitant with the intermittent feeding on to the anode of chunks of the particular metal, or of a wire formed of the particular metal may be effectively avoided.

In the preferred form of this invention particularly satisfactory results have been obtained by utilizing the radiant heat of the anode for vaporizing the powder of the particular metal. This procedure has been preferred in view of the fact that nearly all of the power input into the arc must be dissipated at the anode, consequently there is available at the anode heat energy equal nearly to the total power input. Furthermore by utilizing a portion of this energy for vaporizing the particular metal it is also possible to increase the total power input into the arc and thereby increase the total ion output thereof. That this advantage is achieved in the present invention will be apparent when it is considered that the flow of the particular metal past the anode for the removal of the radiant energy therefrom is more effective in dissipating this heat energy than the vaporization of small quanities of metal deposited directly on the anode.

In practice, the best results have been achieved by having the powder of the particular metal fed through a hollow cylindrical arc anode to be vaporized by the radiant heat from the inner walls of the anode and to be ionized by the electron bombardment of the vapors thus produced within the arc region. In this manner the powdered source metal is prevented from making a direct physical contact with the arc electrodes and is prevented from forming an alloy with the metal of these electrodes to lower their melting temperature. The present invention is also characterized by a further advantage over the metal chunk or metal wire feeding apparatus in that the powder may be fed continuously thus eliminating the abrupt changes in the arc characteristics that accompany the intermittent feeding of the metal chunks or the metal wires.

It is an important object of the present invention therefore to provide an arc discharge affording an abundant source of selected isotope ions that is stable in operation for long periods of time without deterioration of arc electrodes or their supporting structures.

It is a further object of the present invention to provide an improved method of producing gaseous ions of a material that is normally solid and vaporizable under the vacuum only with the application of high temperatures that comprises introducing into an arc discharge a powder of the said material, to vaporize said powder by the heat energy of the arc particularly the radiant heat of the arc anode and to ionize said vapors thus produced by electron bombardment within the arc discharge.

It is a still further object of the present invention to provide a source of ions for an ionic isotope separating apparatus wherein contamination of the arc source of electrodes is avoided and wherein the material to be ionized may be fed continuously.

The above and other objects and advantages of this invention will become more apparent from the following description of a presently preferred embodiment of the invention including also certain novel electrode structure illustrated in the annexed drawing wherein:

Figure l is a generalized and largely diagrammatic view chiefly in section of the ion source of the present invention positioned within the isotope separating apparatus;

Figure 2 is a more detailed elevational view of the ion source of the present invention shown largely in cross section, the section being taken on lines 2-2 of Figure 3;

Figure 3 is a plan view of the apparatus shown of Figure 2; and

Figure 4 is a wiring diagram of the ion source of the present invention.

Referring now to the drawings, and more par ticularly to Figure 1, there is shown, in more or less diagrammatic form, one way of employing an ion source unit embodying the novel features of the present invention (shown in detail in Figures 2 and 3), in anion utilization apparatus such as an isotope separator to provide a copious supply of ions needed in its operation, the isotope separator serving also to complete the evacuated enclosure for the ion source. As illustrated, the ion source unit includes a box-like enclosure IQ for supporting its arc electrodes in a central position relative to the separator tube 5 so that the gaseous ions generated in the are established between the arc electrodes which include an indirectly heated arc cathode H and the cylindrical arc anode [2 will be centered substantially relative to the longitudinal axis of the separator tube. More particularly if the separator tube or the chamber containing other ion utilization apparatus is cylindrical as illustrated in the drawing, the side wall I3 of the box-like enclosure I!) may be semi-cylindrical and the end wall I 4 semicircular to conform to the configuration of the tube.

In any event, it is preferred to have the ion generating apparatus including the previously mentioned arc electrodes supported within the box-like enclosure by means of a liquid cooled end plate i5 which is shown sealed and secured respectively to the top cover IS of the box-like enclosure is by means of gasket H and a plurality of machine bolts of which those indicated by reference numeral [8 are representative. The are electrodes H and i2 are supported in this end plate l5 which may be of brass or other material having a high thermal conductivity, by means of insulated and sealed lead-in conductors to be more fully described later in connection with Figures 2 and 3, which more clearly illustrate certain details of construction of the ion source. The supporting lead-in conductors for the arc electrodes center the arc electrodes relative to the axis of the circular end plate I5, so that the cylindrical anode is supported with its axis vertical and passing through the center of the plate [5, and the platform cathode II is supported horizontally directly beneath the arc anode with the orifice formed therein by the spacing of the groups of rods 45, of which the platform is constructed, on each side of the vertical axis of the cylindrical anode.

A central opening I9 is drilled in the end plate iii to provide a conduit or passageway for the flow therethrough of the powdered material that is to be vaporized and ionized Within the arc in accordance with this invention. As illustrated, this powdered material is adapted to be contained within a cylindrical reservoir or magazine 2| supported vertically above and coaxial of the drilled opening !9 of the end plate l5. This reservoir or magazine is in turn contained within the evacuated enclosure 20 formed by the vertically extending cylindrical wall 22 that is preferably integrally formed with the end plate 15. A cover plate 23 of steel or other magnetic material is shown provided with an integral cylindrical projection on its inner surface for forming a central core 24 for a magnet coil 25. This magnet coil may be secured to the core and cover by having its outer magnetic sheath 26 welded or otherwise securely fastened to the under surface of said cover; which, as illustrated, is also secured and sealed to the end surface of the cylindrical wall 22 by means of a gasket material 2i and end bolts 28.

The core 24 of the magnet coil 25 is terminated short of the end of a spool 29 upon which the coil is wound, to provide a cylindrical space in the magnet coil 25 for the insertion therein of the cylindrical powder reservoir 2|. This resvoir which is adapted to contain the powder of a material comprising the ions that are desired, consists specifically of a cylindrical tube 38 of a suitable lightweight metal, such as aluminum, for example, having a soft iron plug 3| closing one end thereof and a brass plug 32 closing the other end, namely that end which projects exteriorly from the spool 29. This brass plug 32 is shown provided with a metering jet 33 for limiting and controlling the rate of flow therethrough of the powder material contained within the reservoir 2|. As is clear from Figure 2 this metering jet communicates with a larger centrally formed orifice 34 which is designed to collimate the particles flowing therethrough Without clogging.

The soft iron plug 3! is positioned at the end of the cylindrical tube 30 opposite the brass plug, namely the end that projects into the magnet coil 25 so that the reservoir may be suitably agitated by the application of an alternating current to the coil 25 through the lead-in wires 35 which are sealed in a plug 36 to maintain the airtight integrity of the enclosure 20 defined by the vertical cylindrical walls 22 and the cover plate 23. The agitation thus transmitted to the reservoir prevents clogging of the metering jet 33 and provides a controlled continuous flow of the powdered material through this metering jet and through the opening I9 formed in the end plate [5, so that the powder of the material, the gaseous ions of which are desired, may flow freely through the cylindrical anode ii to be vaporized by the heat radiated from the side wall thereof without contacting the anode. The vapors produced by the vaporization of this powdered material flow into the arc region and are there ionized by electron bombardment; and the ions so formed are withdrawn from the region of the are by the electric field established between the arc electrodes and a suitable accelerating electrode represented for simplification by the cylinder 31.

The ions flowing through the electric field established between this cylindrical accelerating electrode and the are electrodes by connecting the latter to a source of high positive potential (of the order of 10 to 20 kv.) relative to the former, are accelerated to a very high velocity to pass in beam-like form through a slot 38 cut, stamped or otherwise formed in the cylindrical shield 39 of the ion source unit to pass axially down the evacuated tube 5.

In order that the arc electrodes of the ion source of the present invention may be maintained at a high positive potential relative to this accelerating electrode 31 to provide the accelerating field for the ions, formed from the vaporization and ionization of the powder in the arc discharge, the end enclosure plate 40 of the box-like enclosure I6 is made to have a configuration that conforms to that of the separator tube 5 so that the box-like enclosure for the ion source may be supported by an intermediate cylindrical sleeve 6 of insulating material such as quartz or porcelain, and the ion accelerating electrode 3'! may be supported without insulation in the metallic cylindrical side walls of the separator tube 5 which is maintained at ground potential.

It is to be understood that the specific means shown for supporting the ion source within the separator tube is illustrative only, it being desirable merely, to show that the ion source is preferably supported within the tube in insulated relationship therewith, so that it may be maintained at the high potential of the accelerating voltage. By so insulating the ion source it is possible to ground the remainder of the separator tube to provide the field-free region for the flow therethrough of the ions withdrawn and accelerated by the electrode 31.

Referring now to Figures 2 and 3 of the drawing wherein certain features of the invention are shown in more detail than in Figure 1 it will be noted that the cylindrical anode I2 is a helix of closely wound Wire of a suitable refractory metal, preferably tungsten, and is supported in the evacuated region by having its ends secured within a block 32 of brass for example, by being hard soldered into suitable recesses provided therein. This block 42 is supported by means of a hollow lead-in conductor 43 insulated and sealed to the end plate I5 by means of the bushing 44. The cathode ll consists of a platform of parallel tungsten wires or rods 45 supported in two groups to lie side by side transversely of two parallel and spaced apart rods or bars 16, also of tungsten, each of which have their opposite ends recessed in suitable rectangular blocks cl supported by the cooling coil 48. This cooling coil is connected into the hollow lead-in conductor as so that a liquid coolant may be circulated through the inner squirt tube (not shown) supported coaxially within the outer hollow lead-in conductor, to traverse this coil 58 and return to its source through the annular space between this squirt tube and this outer hollow lead-in conductor.

The cooling fluid thus circulated through the supporting coil for the horizontal platform cathode is effective in removing heat from the two rather massive rectangular blocks 4? that support the parallel rods 46 upon which the tungsten rods 45 of the cathode lie. Thus, the ends of the rods or wires 45 that form the cathode may be effectively cooled and the electron emission over the region of their contact with the transverse parallel rods 46 may be minimized or otherwise controlled. More specifically in the embodiment illustrated a group of four of the tungsten rods 45 are supported to lie parallel and side by side transversely of the rods 45 on each side of the anode axis so as to provide an orifice or opening M within the cathode platform H directly beneath the cylindrical anode. A filament formed preferably of tungsten or other material having good thermal electron emissive qualities is positioned directly beneath this platform cathode I2 to extend substantially parallel to the supporting strips or rods 56 but at a position off the vertical axis of the anode and cathode opening 4i whereby to be shielded from the anode by the platform H. Each end of this filamentary cathode is supported by its respective lead-in conductor 52-53.

As will be clear from the drawing, the leadin conductors 5253 for the filamentary cathode as well as the lead-in conductor 50 for the pla form cathode and the lead-in conductor 43 for cylindrical anode are preferably formed of copper tubing and, as will be noted in the crosssectional showing of the lead-in conductor 53, are provided with a secondary tube 54 which is supported concentrically therein for permitting the flow of cooling fluid through these tubes to remove the heat from the ends of the filamentary cathode where they contact the lead-in conductors. As illustrated the filamentary cathode 5| is secured to its respective leadin conductors by having its ends inserted in a suitable opening drilled in a respective one of the cylindrical blocks 55 that are welded to the end of the lead-in conductors fol-53; and are therein held in place by means of the set screws 58 for example. Since a suitable heater voltage must be applied to the filamentary cathode and further since an accelerating voltage for the electrons must be applied between the filamentary and platform cathode for causing the electron emission of the filament to bombard the platform to heat the platform cathode to electron emissive temperatures, and further since suitable are potential is to be applied between this platform and the cylindrical anode it is apparent that the four lead-in electrodes must be insulated from each other and are thus each insulated and sealed from the end plate 15.

Although any number of insulated seals known to the prior art may be used for these electrodes one remarkably successful seal, is illustrated in cross section in Figure 2. This seal consists essentially of a metallic insert 51 in the form of a cylindrical bushing which is soldered or otherwise securely retained in a drilled opening in the end plate H5. The end of the insert 51 extending to the high pressure side of this end plate I5 is internally threaded to receive a packing gland 58, whereas the inner end of the bushing that is flush with the inner surface of the end plate I5 is provided with a projecting flange or shoulder 59. Interposed between the lead-in conductor 53 and the metallic insert 51 are two insulated bushings 5i} andiil at least the former of which is formed of a refractory material. Bushing 60 of refractory material is fashioned with a section of enlarged diameter into which the uniform diameter portion of the insulated bushing 5| may be inserted. The sealing ring 62 is interposed between the end surface of the bushing GI and the inner shoulder of bushing 60. So also is a sealing ring 63 placed at the end of the bushing 65 between a shoulder formed by the enlarged portion thereon and the shoulder 59 of the metallic insert 51. Ihe bushing 51 has a flange or enlarged cylindrical portion which is adapted to be engaged by the end surface of the packing gland 58 through the sealing ring 54 so that when the gland 58 is screwed down it respectively compresses the sealing ring 65 against the foregoing opposing flange surface of the bushing 5!, the sealing ring 52 between the end surface of the bushing 6i and the inner flange formed by the enlarged section of the bushing 60, and the sealing ring 53 between the outer flange surface of the bushing 55 and the inner flange surface '59 of the metallic insert.

As noted hereinabove it is proposed to have each of the lead-in conductors for the respective arc electrodes provided with a squirt tube such as 54 for circulation through each of their respective hollow lead-in conductors of a suitable cooling fluid. Accordingly suitable squirt tube glands 65, t6, 6'! and 68 are provided respectively to the lead-in conductors 43, 50, 52 and 53 for supplying and circulating this cooling fluid. While any number of sealing glands could be used one type of gland that has been found satisfactory is illustrated in cross-section in Figure 2. The gland 68 is shown as comprising a cylindrical body member 18 having an opening drilled at one end thereof for supporting a tube H communicating with the inner squirt tube 5 to provide a conduit that may be utilized as a supply for the cooling fluid. The squirt tube 54 is supported within the body member 0 by a push fit in a small opening i2 that communicates with the opening into which the tube ll is secured. The tube 13 which may be the return conduit for the liquid coolant is connected into the side of the body member 10 by being soldered or brazed into a suitable opening 7 drilled therein. This opening 74 communicates with a larger coaxial opening '75 drilled in the body member 70 communicating with the interior of the hollow lead-in conductor 53 which is supported in the body member by means of a threaded cap 16 and rubber gasket 'il'. Thus by circulating the liquid coolant down the inner squirt tube 56 and up the space 69 between the coaxial tubes, the heat conducted to the ends of the cathode may be removed to prevent the cathode so supported from attaining a temperature at its support sufficiently high to cause a warping thereof.

It may be noted also from the drawing that openings 18 in addition to opening iii are drilled into the end plate I5 to communicate with the evacuated space 20 formed by the upstanding wall 22 and the cover plate 23 to provide for the continuous evacuation of this space through passageways other than the conduit for the supply of the powdered material. .Since it is desirable in the operation of the apparatus disclosed to keep the end plate I5 cool to reduce the tendency of the powdered material to clog the opening IS a cooling tube. i9 is shown supported by this end plate at its outer periphery. Furthermore, a radiation shield is shown provided intermediate the anode l2 and the end plate it to shieldthe opening l9 from the radiant heat of the anode surface since it has been found in operation that it is desirable to support the anode as close as possible to the powder reservoir metering ofiice 33, to have the powder particles pass through the cylindrical anode at relatively low velocity to increase the duration of the passage through the anode to thereby increase the time during which they are subjected to the heat energy radiated therefrom. It is also noted that the filamentary cathode 5! is supported off the axis of the anode l2 and that the platform cathode l l is provided with a central opening so that any powder not volatilized in its path through the anode will fall through this opening in the platform cathode to pass on down into the evacuated region of the tube 5 without contacting either the platform arc cathode or the filamentary cathode.

It has been found from prior experience that a filamentary arc cathode becomes contaminated with the source metal after continuous operation, because of its exposure directly to the anode where the source metal is being vaporized, and such contamination, plus the positive ion bombardment, cause the filament to burn out after a relatively short operating time. Accordingly it is preferred in the embodiment illustrated in this invention to utilize an arc cathode that is indirectly heated by the electron bombardment from a filament positioned directly beneath the platform cathode but out of the region of the arc and out of the region where serious contamination with the source metal vapors takes place. Furthermore there are other advantages to be obtained in utilizing an indirectly heated arc cathode as distinguished from a filamentary arc cathode and these advantages may be found specifically set forth in the copending application Serial No. 350,313, filed April 24, 1953, coveringv ion sources employing indirectly heated arc cathodes.

An ion source embodying the features of the present invention has been constructed and operated wherein the anode I2 takes the form of a helix of closely coiled 6Q mil tungsten wire having an inner diameter and a length of along the axis. The coiled anode i2 is supported with its axis vertical as illustrated in the drawings. The platform cathode l l consists of eight 100 mil tungsten rods 45 supported on a pair of 100 mil tungsten rods 46 in groups of four, parallel and side by side, the groups being spaced apart, however on opposite sides of the anode axis to provide an aperture il therein as seen in Figure 2 for the passage therethrough of the powder dropped along the axis of the anode but not vaporized by the heat radiating therefrom. At a distance of about 1%" below the arc cathode a straight filament 5i also of 100- mil tungsten is supported in a position off the axis of the anode to complete the electrode structure.

The feeding of the arc with the powdered material to be vaporized and ionized is accomplished by causing a steady stream of this powdered source metal to be fed through an aperture 19% in diameter drilled in a liquid cooled end plate which is protected from the are by a radiation shield 80. The feeder and powder magazine 2i consist of an aluminum cylinder 30 with an iron top 3| and a brass bottom disc 32 in thickness. The center of the bottom disc is provided with a metering jet 33 that is 0.026" in diameter for the top ,4, of the disc 32, but is increased to 0.031" diameter for the remaining distance to provide a collimating orifice 34". The smaller hole 33 thus limits the rate of flow of powder and the larger cylindrical section 34 is designed to collimate the particles without clogging. The feeder, consisting of this cylindrical tube 30 and magnetic end plug 3!, is inserted in a suitable magnetic circuit, substantially of the type illustrated in the drawing, and made to vibrate along the vertical axis thereof by means of a 60 cycle alternating current. More specifically, a ferro-resonant circuit 98 may be advantageously used for the coil 25 of the electro-magnet in order to get high peak current of low R. M. S. value. This feeder comprising the reservoir 2| and circuit 96 was found to operate satisfactorily with the magnet current controlling the feeding rate over a wide range.

In an ideal operation the powder drops from position of rest above the anode and on the anode axis and flows freely by gravity through the anode and is either vaporized while in the anode space or drops into the receptacle below the arc electrodes. Experiments seemingly indicate that the powder was actually vaporized by radiation during its fall through the anode. This explanation of the operation is given weight by the fact that when the cylindrical anode is rotated about a vertical axis through its support the arc current is increased and then drops to zero as the rotation in either direction from a central position is continued. It seems probable, therefore, that at first when the powder fell nearer the anode wall a larger fraction of the powder supplied was vaporized until the position was reached at which the powder struck the anode walls and the arc went out. It is not proposed, from the above explanation of operation, that this invention be limited or bound by any particular theory or theoretical understanding of its operation however, since the procedure and apparatus illustrated in the specification have been found by test to operate very satisfactorily in the manner described and it is unnecessary therefore to set forth the theory in support of its operation. It does definitely appear however, that the powdered material is actually vaporized by the radiation during its fall through the anode and accordingly this would account for the fact that contamination of the arc electrodes by the metal itself seems to be virtually eliminated.

Considering now the general principle of operation of the ion source unit, there is shown in Figure 4, a schematic wiring diagram that may illustrate the principle of operation of the invention and particularly the principle of operation of the electron source and the ferro-resonant circuit for the magnet coil. As illustrated current is supplied to the filamentary cathode 5| through the transformer 8| the primary 82 of which is powered from a variable auto transformer such as the variac 83 to provide a variable source of heater current for heating the filament to an electron emissive temperature. The electron emission from the filament is accelerated and made to bombard the platform cathode l l with a high velocity by connecting the platform cathode to a source of potential 84 that is positive relative to the filamentary cathode 5|. After the bombardment of the platform cathode has been effective for a suificient period of time to raise the temperature of the cathode to increase its electron emission the source of are potential shown as comprising a high positive potential portion of the high voltage source 85 is applied to establish ii an electron controlled are between the coiled anode and the platform cathode.

Now, since substantially all or the energy supplied to the arc must be dissipated in the form of heat at the anode, it is evident that the anode will attain a very high temperature in dissipating the are energy. After the anode has attained this high temperature, power from a variac 86 is supplied to the primary t? or the transformer 88 to energize the transformer secondary 88 which is connected in the form-resonant circuit 53 of the magnet coil 25 to provide the power necessary for suitably agitating the reservoir 2| to pro-- vide for the continuous fiow of powder through the coiled anode. The powder thus projected into region of the anode is vaporized by the heat energy radiating therefrom and the vapors thus produced or subsequently ionized by electron bornbardment within the arc discharge. To provide for the withdrawal and acceleration of these ionized particles the accelerating electrode 3! is shown connected to the high voltage source 85 through the lead 94 to make this electrode highly negative relative to the positive source potential. It will be clear from the wiring diagram of Figure 4 that the electric circuit connecting the magnet coil 25 to the secondary 89 of the transformer 88 has connected therein in series relation the resistance 9|, the capacitance c2 and a saturable inductive reactance 93.

It has been known for some time prior to the present invention that certain unusual resonance efiects occur in circuits of the type illustrated in Figure 4 wherein the inductance 93 is adapted to saturate within the normal range of operation of the circuit. If the circuit elements as above enumerated are connected in series and properly dimensioned it will be observed that for a gradually increasing applied alternating voltage, of constant frequency, the efiective current is not proportional to voltage but increases critically at a certain voltage. Similarly, for a gradually decreasing voltage, at constant frequency, the effective current decreases abruptly at a certain voltage. When a series circuit of this type is energized by a voltage that is slightly higher than the critical voltage for the higher current condition, and when any one of the impedance elements, which may be either the resistance 9|, the capacitance 92 or the inductance 93 is varied a relatively small amount an abrupt decrease in current in the circuit is obtained, similar to the abrupt decrease in current that is obtained for a gradually decreasing applied voltage.

In the U. S. Patent No. 2,040,677 as in the present invention, advantage is taken of the change in inductive reactance that accompanies the movement of a permeable core, into the magnet coil that is connected in series with the saturable reactance, the capacitance and the resistance, and to which is applied a voltage that is adjusted to a value slightly higher than that necessary to obtain the high current condition; to produce a change in impedance in the series circuit, sulficient to cause the current therein to be suddenly decreased to the low current condition. The core 3| of the reservoir may thus be made to oscillate at a period determined, predominantly by the mechanical properties of the moving element and only partially by the resonant characteristics of the circuit 99.

The core 3| of the magnet coil 25 secured to the reservoir 2|, is shown partially withdrawn from the magnet coil 25 to cause the circuit 90 to be resonant, producing a current of high magnitude. This high magnitude current is ef' fective in pulling the armature 3| up into the magnet coil 25 causing the inductive reactance of the magnet coil to increase. This change in inductive reactance in the circuit caused by the movement of the armature core 3| is adapted to render the series non-linear circuit dissonant. When this occurs the circuit current decreased abruptly to a relatively low value and the core 3| is withdrawn from the coil by gravity. This cycle of operation is repeated automatically in such a manner that the eiiective current in the circuit rises and falls in a pulsating manner and the reservoir 2| is in continual reciprocation to shake the powdered material out through the metering orifice 33 to provide a substantially continuous flow of this powdered material through the anode l2. That the rate of flow of this feed may be governed, the ferro-resonant circuit 99 is shown energized by the secondary 89 of the transformer 88 the primary 8'! of which is connected to variac 86. Suitable adjustments of the variac will control the magnitude of the alternating voltage applied to the ferro-resonant circuit and will control the power input into the magnet coil during each cycle of oscillation to govern the material fed as a result or" each impulse.

Thus it is apparent that there is illustrated and described in this specification a preferred embodiment of this invention that is operable to continuously supply a predetermined quantity of the vaporizable material into the region of arc discharge, at controllable rates, and adjacent the anode, so that said material may be vaporized by the radiant heat therefrom without actual contact with the anode or other are electrodes and the vapors thus produced may be ionized by the electron bombardment within the are discharge to produce a copious supply of gaseous ions for use in a suitable ion utilization apparatus. It should be understood however that the detailed description of the presently preferred embodiment of this invention is set out above only so that others may readily understand how to achieve the good results and objects of this invention, with the reservation that changes in the construction and combination of parts may be made without departing from the spirit and scope of this invention as defined in the subjoined set of claims.

I claim:

1. Apparatus for producing gaseous ions of a predetermined substance, comprising a plurality of electrodes adapted for establishment of an ionizing nd heat-producing discharge therebetween; means for advancing into the vicinity of one of said electrodes, but out of contact with said electrodes, finely divided material comprising said substance, to be vaporized by heat resulting from said discharge and to be ionized by the discharge; and means for withdrawing the produced ions from the vicinity of said electrodes.

2. An apparatus for producing gaseous ions under vacuum comprising in combination, an evacuated chamber, a hollow cylindrical anode disposed within said chamber with its axis in a vertical direction, a cathode positioned within said chamber below said anode, means for establishing an arc discharge between said anode and said cathode, means for continuously dropping a powder of the material the ions of which are desired from a position vertically above said anode along the axis thereof whereby said powder will fall freely through said anode to be 13 vaporized by the radiant heat from the side walls thereof and the vapors thus produced will be ionized by the electrons within said are, and means for withdrawing the gaseous ions of said material from said are discharge in a direction substantially normal to the axis of said anode.

3. The combination defined in claim 2 further characterized by the fact that said cathode is provided with a central orifice in alignment with axis of said anode to provide for the free passage therethrough of all particles of said powdered material not vaporized in their flow through said anode, thereby to avoid contamination of said cathode by said powdered material.

4. An apparatus for producing gaseous ions under vacuum comprising in combination, an evacuated chamber, a thermally electron emissive cathode therein, an anode having a vertical channel disposed in said chamber in a position directly above said cathode, means for establishing an arc discharge between said anode and said cathode, means within said chamber for continuously supplying a stream of nongaseous material through said channel in said anode to be vaporized by the radiant heat from the walls thereof whereby said vapors will pass into said are to be ionized by the electron emission from said cathode, and means for continuously withdrawing said ions from said are region.

5. An apparatus for producing gaseous ions under vacuum comprising a chamber sealed at sub-atmospheric pressure for housing an anode, a cathode and a reservoir for containing a powdered material of the ions that are desired,

said reservoir having an orifice therein positioned above said are anode, means for agitating said powder to provide for its continued emergence through said orifice to fall by gravity into the region of said anode but out of physical contact therewith to be vaporized by the heat of the arc dissipated at said anode and subsequen ly ionized by the bombardment with the electrons of said are discharge and means for withdrawing said ions from the region of said are discharge.

6. An apparatus for producing gaseous ions under vacuum including in combination a chamber sealed at sub-atmospheric pressure enclosing an anode, a cathode, and a powdered material the ions of which are desired, means for establishing an arc discharge between said anode and said cathode and means for continuously feeding a controlled amount of said powdered material into the region of said are to be vaporized by the heat of the are without contacting said anode or said cathode, and to be ionized by the electrons within said are whereby a continued production of gaseous ions of said material may be obtained.

7. An apparatus for producing gaseous ions under vacuum including in combination a chamber sealed at sub-atmospheric pressure enclosing an anode, a cathode, and a supply of powdered material the ions of which are desired, means for establishing an arc discharge between said anode and said cathode, and electro-magnetic means for continuously feeding said powdered material into the region of said are to be vaporized by the heat of said are without contacting said anode or said cathode and to be ionized by the electrons within said are discharge whereby a continuous production of gaseous ions may be obtained.

8. The combination defined in claim 7 above characterized further by the addition thereto of means comprising a ferro-resonant circuit for controlling the electro-magnetic means whereby 14 a wide range in the rate of feed of said powder may be obtained.

9. An apparatus for producing gaseous ions under vacuum including in combination a chamber sealed at sub-atmospheric pressure enclosing an anode, a cathode and a reservoir containing a supply of powdered material the ions of which are desired, means for establishing an arc discharge between said anode and said cathode, and electro-magnetic means for agitating said reservoir to continuously feed a controlled amount of said powdered material into the region of said are to be vaporized by the heat of the are without contacting said anode or said cathode and to be ionized by the electrons within said are discharge whereby a continued production of gaseous ions may be obtained.

10. The combination defined in claim 9 above characterized further by the addition thereto of means for controlling the current to said electromagnetic means whereby a wide range of control or" the rate of feed of said powder may be obtained.

11. An apparatus for producing gaseous ions of material under vacuum comprising an evacuated chamber, a platform cathode comprising a plurality of parallel wires supported side by side and horizontally within said chamber, a hollow helical coil anode disposed vertically within said chamber above said cathode, a filamentary cathode beneath said platform cathode and a reservoir adapted to contain a powder comprising material the ions of which are desired positioned within said chamber above said anode, and means providing for the continuous flow of said powder vertically through said anode without contacting the side walls thereof.

12. An apparatus for producing gaseous ions of a metal under vacuum comprising in combination an evacuated chamber, a platform cathode comprising a. plurality of parallel wires supported side by side and horizontally within said chamber, a hollow helical coil anode disposed vertically within said chamber and above said platform cathode, a filamentary cathode supported beneath said platform cathode and shielded from said anode, a reservoir adapted to contain a powdered material comprising the substance desired to be ionized, means for rendering said filamentary cathode electron emissive, means for bombarding said platform cathode with the electrons emitted from said filamentary cathode to cause said platform cathode to be heated to an electron emissive temperature, means for establishing an arc discharge between said platform cathode and said anode, and means for providing a continuous flow of said powder vertically through said anode without contacting the side walls thereof to be vaporized by the heat of the arc dissipated in said anode and ionized by electron bombardment of said vapors within said arc.

13. An apparatus for producing gaseous ions of a metal under vacuum comprising in combination an evacuated chamber housing a thermally electron emissive cathode, an elongated anode disposed with its longitudinal axis vertical and above said cathode and a reservoir positioned vertically above said anode for containing a pulverized material of the ions that are desired, said reservoir having an exit orifice for the flow therethrough of said pulverized material, said anode and said cathode being formed of a metal having a, melting temperature higher than the vaporization temperature of said material but alloying with said material to lower said melting temperature by an amount dependent upon its 15 concentration; said anode being provided with a vertical opening extending longitudinally therethrough and substantially coaxial with said orifice to form a passageway through which said material may fiow without contacting the side walls thereof, means for connecting said anode and cathode in a circuit to establish a flow of electrons from said cathode to said anode to heat said anode whereby said material flowing freely through said passageway will be vaporized by the radiant heat from the side walls thereof, and ionized by the bombardment of said vapors by 16 the electrons in their paths from said cathode to said anode.

14. The combination defined in claim 13 above characterized further by the fact that said cathode is also provided with an opening therein substantially coaxial with said passageway to prevent any nonvaporized material flowing through said anode from contacting said cathode to form an alloy therewith to lower its melting l0 temperature.

No references cited. 

